Implantable medical leads are devices that couple electrical pulse generators to cardiac muscle. They are commonly used for delivering an electrical pulse to the cardiac muscle, for sensing electrical signals produced in the cardiac muscle, or for both delivering and sensing. Many complex medical devices utilize implantable leads. Pacemaker systems are used to treat bradycardia (i.e., abnormally slow heart rate) and other heart arrhythmias. Typical pacemaker systems include an implantable pulse generator and one or more leads which form the electrical connection between the implantable pulse generator and the heart. Implantable cardioverter defibrillators (“ICDs”) are used to treat tachycardia (i.e., abnormally rapid heart rate). An ICD also includes a pulse generator and one or more leads to deliver electrical energy to the heart.
Implantable leads typically include a flexible conductor surrounded by an insulating tube or shaft that extends from an electrode at the distal end to an electrode at the proximal end. Some known leads include a relatively flexible distal end with a relatively stiff proximal end. The stiffer proximal end allows the lead to be pushed and rotated through the vascular system while the flexible distal end allows the lead to maneuver around physical obstructions, tortuosities and take-off angles. The shift from the stiff proximal end to the flexible distal end is often abrupt. This abrupt shift from a stiff portion to a flexible portion often results in the lead prolapsing, or folding, when the lead is guided into a branch vein, such as a coronary branch vein. Thus, there is a need in the art for a medical lead that gradually transitions from a stiff proximal section to a flexible distal section.